Hydraulic control for steering clutches



Feb. 16, 1954 Q BANKER 2,669,330

HYDRAULIC CONTROL FOR STEERING CLUTCHES Filed NOV. 5, 1948 3 Sheets-Sheet l Feb. 16, 1954 l o. H. BANKER HYDRAULIC CONTROL FOR STEERING CLUTCHES 3 Sheets-Sheet 2 Filed Nov. 5, 1948 su s Q' f, ma M I f lmn r n@ Q m a N l Q M /Nmkw www mm@ C mn Q QW.

Feb. 16, 1954 o, H, BANKER 2,669,330

HYDRAULIC CONTROL FOR STEERING CLUTCHES Filed NOV. 5, 1948 5 Sheets-Sheet 5 Patented Feb. 16,` 1954 VHYDRAULIC o oN'rRoL -FoR STEERING `CLUTCHES .Gsjcar H. Banker, Evanston,

@Products fCorpor-ation,y

tion o'f Delaware ,111., A-assignor nto ew Chicago,- Ill., a corpora- 4Applifatimn November 5, 1194s, :serial No. 258,114

zkclaiims.

, -heipresent invention pertains lto an :improved ,hydraulically .ccntrolled, 'steering lclutch Ymecha- Llnism and :to -an improved-valve "for variably-drop- :ping the hydraulic :operating pressure to provide .for a yvariable torque, .slip-'drive .operation of said mechanism.

-f 'Conventional hydraulically :controlled clutch and'irelated mechanisms which l-employ Vthe principle of providing a variable hydraulic operating pressure, operate on the theoryuof :building 'up ythe hydraulic :pressure from a Aminimum to ,ffull .line pressureinzthe :coni/rol 'cylinder of said mechanism`,`to 4thereby A:accomplish a variable slip-drive throughxthexlatter mechanism. In contrast to #this ,inode 4of operation; the operation rof the preslerrt .mecha-mism, zas .preferentially embodied in :a steering clutch :for tractor type vehicles, is based on thecprinciple 'of effecting :a :graduated reducv-tion o'r dumping yof :the Apressure `effective :on fce'rn tainifriction elements of the control mechanism ,from normal, fulL'zclutch-operating, :line pressure, in which a direct non-slip .drive is accomplished, -fto zero, fully dumped pressure. f-'Inzisaid lastiacon- :dition ysaid frictionielements :are operatively devcoupled fromzoneanother. .The pressure isgradyiiailrly vdiminished by 'means ofr an v.improvedvar-'iable pressure reduction valve 'under 'the manual lcontrol rof. an operator to .produce any fdesired fdegree ofr :clutch slip.

.ifMy copending application xSerial No. f77-8,382, `riledfzoctober .7, 19:47, 'now Patent No. 2,580,381, illustrates and describes a ,planetary type; driving and `steeringA mechanism -for tractors ordi'ke crawler-type vehicles,@characterized bythe fact that .the y"degree fof Lturn :of endless tracks Sis controlled,v as .in-the present application, .by the .gradual release of the hydraulic :liquid which .is normally effective on .a fc-l'utch .of said mechanism from ,full line pressure domi to a zerczpressure, fullydnmped condition. .Thegfgraduated pressure reduction valve yWhich constitutes vthemain subject matter of the pres` ent invention is particularly well suited for-application to a drivin-grand steering mechanism ,of this type. n

Itisanobject of theinvention to provide a friction` driving or like mechanismpf, atype .is controlledin` `the .operation thereof by va'riably reducing the hydraulic pressure operative on certain friction 4elements thereof, in comfbination KAvir/ ith an improved, graduated pressure 'reduction valve adapted jto effect the desired.

gradual dumping of-fthe "hydraulic control or operatingliqu'id forfthe purpose referred Cto.

i A 'ino' 'thercbject the vehicle on its i off the invention :is .to provi-de es a .pressurereduction valve of :the Yforegoing type, adapted tothe manually controlled by an operator to effect the aforesaid gradual release of pressure, which valve .is simple, :sturdy and .inex- .pensivegiinits parts, yet `adapted :for a long -life of-:satisfactory operation "with vlittle 'or fno atten- -tion or maintenance.

More specifically, it :is *an object of `the invention to provide a graduated pressure reduction valve including a valve housing adapted to be lconnected :between a pump -or gli-ke source of 1hydraulic pressure and va mechanism vto be varia-bly controlled by select-ive reduction of pressure operative thereon,` 'and a pair of coaxial, telescoped valve felements :said housing which are 'subject tofpr'essure from :said Jso'urce :and .are adapted to be manually controlled in a fashion to profgnessively dump-:hydraulic rliqlflidffrom said mechanism; :said elementsy being automatically Vshiftable relativek to one another under the inuence of )hydraulic-pressure from 4said source :actingin opposition to a predetermined spring load, being manually controlled by thegoperator to produce :a desired variable decrease `pressure effective fon-esaid mechanism.

A'notl'iei-fspecc :object 'of the invention is to provide a reduction valve .including a pair of valves fan'dby-pass elements ymounted for coaxial relative fmoveinentin a valve housing, vone there- .of-being rspringurged .in its movements in opposition to the pressure of hydraulic liquid from a suitable .fsource and the other thereof being manually actualole by an operator in opposition to lsaid pressure Yvvhereby 4to optionally expose lor Vclose 'a.ibylpa'sspath between .said elements for the graduated 'release and dumping of hydraulic :pressure as ;:desire`d.

A still further object is to provide ,a .hydrauliica'llycontrolled:driving clutch :assembly which is particularly well adapted forinstallaton in endless track laying vm'el'iicles to afford a Wide range of steering-or'turnin'g radii, ranging from .a very gradual turn` to :a dead track turn 'or r'full pivot, wherein .a pairfof like assemblies controlling the respective 'tracks' fof the .vehicle each includes an vindividual, variable 4.pressure ydropping control valve .bf'thesort referred to above, said'valves -beingsuppliedby a common 'source of .hydraulic power-and .having improved vmeans for rendering 'the operation 'of one .thereof and its associated clutch yasseinbl'y totally v.independent of the fop'- *eration` ofi theother-and its assembly, each `of said valves' thereby `"actir'ig as a ,press-ure regi-'1L lator for insuring the'intended rc` peration of the respective other assembly.

but it will be appreciated Another more specific object is to provide a hydraulically controlled, drum type steering clutch employing an association of coaxially telescoped driving and driven members in which novel structural provisions are incorporated to facilitate greatly the dismantling of the clutch for servicing or the like, and subsequent reassembly of the parts. Y

Yet another object is to provide a construction of the foregoing type including a hydraulically operated friction clutch or like unit, a variable pressure dropping control valve for said unit, and a brake operatively associated therewith, together with common operating provisions for said valve and brake whereby the valveis Vvactuated throughout its entire clutch pressure controlling range prior to operation of said brake.

The foregoing statements are indicative in a general way of the nature of the invention, but other and more specific objects will be apparent to those skilled in the art upon a fullunderstanding of the construction and operation of the device.

Two specific embodiments of the invention are presented herein for purpose of exemplication, that the invention is susceptible of incorporation in still other modied forms coming equally within the scope of the appended claims.

In the drawings,

Fig. l is a fragmentary view in vertical, axial section through a hydraulically operated steer-A ing clutch mechanism adapted to be variably controlled by a graduated pressure reduction valve, which valve is illustrated in elevation in its operative, installed relation to said mecha,-

nism;

Fig. 2 is an enlarged view in vertical transverse section through the valve structure illustrated in Fig. l, approximately along line 2-2 oi the latter, showing the parts in Zero pressure position thereof;

Fig. 3 is a somewhat enlarged view in section similar to Fig. 2, illustrating the relationship of the component control elements of said valve in a diiierent, manually controlled, intermediate pressure position thereof Fig. 4 is a View in vertical section through another pressure reduction valve in accordance with a somewhat modified embodiment of the invention; Y

Fig. 5 is a fragmentary, somewhat conventionalized, side elevational view, in vertical section through clutch housing of the mechanism, illustrating the invention as applied in a preferred embodiment to a steering clutch arrangement ior a dual, endless track crawler-type vehicle; and

Fig. 6 is a fragmentary top plan view of the structure shown in Fig. 5.

My copending application Serial No. 778,382 referred to above illustrates and describes a driving and steering mechanism for endless track, crawler-type vehicles, which mechanism embodies a disk-type clutch tary device. This clutch is controlled bythe selective, graduated release of hydraulic liquid normally effective thereon, from a normal, full operating line pressure to a zero pressure, fully dumped condition, in which the clutch is fulliT released. The present invention pertains, in one aspect, to improvements in a valve adapted to eiiect such a graduated pressure reduction. A1- though the valve is illustrated-herein in a preferred dual installation 'controlling' an improved associated with a planef y Referring to Fig. l oi Vshaft I2 holds said drive ring form of steering clutch for endless track vehicles of the type referred to above, enabling a selective slip or non-slip frictional control of either track of the vehicle, it is to be understood that said valve is equally applicable to the driving and steering mechanism of the application above referred to, or to .any other equivalent installation in Which the regulation of a hydraulically controlled clutch or similar component is effected by a graduated reduction of the pressure normally operative thereon.

the drawings, the reference numeral Ill generally designates a disk- Vtype steering clutch of the sort referred to above,A it being lunderstood that this structure is reproduced on 'the opposite side of the central driver for the assembly to be referred to. Corresponding parts of said other clutch are designated by similar reference numerals, primed.

This clutch includes an internal, drum-like driving member II which is drivingly secured to a main drive shaft l2 by means of a drive ring I3 bolted on said drum and keyed or splined at I4 to said drive shaft. A retainer ring bolted to in proper position. Shaft I2 is driven from a bevel gear I5 keyed on shaft I2, and suitablel bearing provisions are made for rotatably mounting the shaft and other components of the assembly in the housing I6 of the structure.

The driving drum I I is provided with external, elongated splines II receiving the friction clutch disks It in a non-rotative, axially slidable relation thereto. Another set of clutch disks I9 is similarly splined at 20 on an external driven drum 2| which is axially telescoped over the internal drum II. An annular abutment 22 is also drivingly engaged `with the splines 20 and is restrained in the axial direction by means of a retainer ring 23 associated with drum ZI in the manner illustrated. A conventional brake band B surrounds drum 2 I.

An annular pressure member 24 is splined to drum 2l at the opposite end of the clutch disk assembly and is normally pressure urged to the right, as illustrated in Fig. 1, to apply clutch engaging pressure on disks I8 and I9. An annular piston 25 is mounted for axial movement in an annular cylinder 26 which is defined by a shaped end plate 21 of the clutch drum assembly, said plate being bolted on the drum 2I for rotation therewith. Piston 25 is appropriately sealed to retain hydraulic pressure in the cylinder rearwardly thereof, as by means of a pair of conventional, annular oil seals 28, and hydraulic pressure is admitted to the cylinder through the inclined passages or ports 29 in plate 2T. An annular, dished Belleville-type spring 30 normally urges the piston 25 to the left, as viewed in Fig. 1, the internal and external peripheries oi said spring being engageable with said piston and with a retainer ring 3I which is nxedly associated with the end plate 21.

Said end plate 21 is shaped to provide an annular bearing recess 32 which receives a cylindrical, hydraulic pressure distributor head 33 iixed in the housing I6. This head is bored to provide a passage 34 through which hydraulic pressure liquid, such as a good grade of lubrieating oil, is supplied to the cylinder-26 by means of port 29. Appropriate annular sealing rings 35 are disposed in-parallel grooves on said head onveitherr side of port29 to prevent leakage of the liquid. A conventional oil sea1`36-is applied "to 'the pressure' distributor head 33 between-the ,litter and a hub extension 31 of 'theshapedidrum 4lend-plate'121'., Ito prevent leakage `at thispoint. 'Said hub is appropriately vsecured lation` to the driven sha-ttm?, which .is mounted *in Adriving' rerby a ball .bearing .39 in the inte-rior of the `hydraulic head 33.

The `passage 34 through which hydlaulic.l pressure is supplied to and 4voided .from the clutch cylinder 26 is communicated withythe.pressure reduction valve of the 'present invention, :genlorally designated .49, or other lconduitdfl, tapped in the hydraulic 33 in the fashion illustrated. The valve d, is .mounted by an appropriate bracket 42 'on asuit- 'able support for iexamplathe clutch housingtlt, :and this bracket may include .a pair of. outwardly extending, laterally spaced, fork-like pivotarms '4d-for a purpose to be described.

Referring now-,particularly to Figs 2 :and 3, .wherein structural details .vor the valve-40 are .illustrated the latter includes a .suitable `chambered and `ported casing 44 iixedly mounted on brackets. 142,. which casing has an internal. axially extending, cylindrical bore 45. :The upper end of ,said bore is closed by a cylindricalplug .4S ,secured therein by a snap ring 47.. This plug .is turn centrally aperturedor. bored for the yslidable :reception of an operating stem. 48, and said stem is adapted to be manually actuated .by the operator' through a bell crank 49 which `is pivoted at I5B on the. bracket arms 43. yOne arm of this :bell vcrank acts asa tappet provided with a'roller. 51 engaging with the `end voffva'lve control stem 48; the other arm'is adapted to be oon- -nected by an element '52 :with any :suitable 'type of operator controlled, manual actuating lever, linkage or the like.

Control stemil extends coaX'ia-lly through 'the valve bore 45 and is providedxat its lower end with a cylindrical,` barrel-shaped, doliblef'seated `valve `element 53. element is adapted .to 'be .manually actuated ldownwardly for -sealing engagement-'of the truste-conical lower valve seat 54 thereof with a correspondingly shaped seating surface 55 in the casing. :Said seat 55.is located at the junction of bore =45 with an :axially aligned, .somewhat .narrower hydraulic infletypassagefii, .hydraulic liquid :being admitted to said inlet ,passage through an inlet fitting .5? `from a suitable pump or other source. vA idlfical :check member 59 controls the Anow of through littingl v5:?, --yielding .rearwardly under line pressure to communicate said t- 4ting Awit-hthe passage .5.5. spring loadingrof the-check .meinber59 .is such that it willyield under `a full hydraulic line pressure'iof, say.,r80 pounds per square inch.

, A cylindrical sleeve-like lbyepass. control valve .element 60 is disposed concentrically of the valve element 53, being disposed in leak-'proof .sliding relation to the valve bore4i5. This byfpass element is provided with a conical valve -seat :6l 'internally' thereof and intermediate itslength, 'for engagement with a corresponding ,conical seat 62 whichV is vcarried von'the end of the valve :element 53 lopposite its aforesaid seat 5f/4. The by-pass valve element- 60 isaxially ,engaged-above said seat 'by a coiled compression springy normally the same `in a direction toengafge the "aforesaid seats WSI., '62, Athis spring abutting ythe plug-4t` at its opposite end.

in'I'he VaIVeeIement :53.is axially .housed within the .by-passelement `0,fbeneath theseat 6l 4of the. latter and within anntegralf depending portionii thereof. ,f A"This skirt portion. .is slotted spring "urged, cylin- .by lmeans of ,a suitable pipe around itsflower extremity.. as indicated yat .56, for normal, ifullpressure communication of liquid .inmassage with a radial port 61-opening to Shore 45. Port-'61 is in turncommunicated :by thelabove described y'connectingconduit -4'l with :thehyldraulic distributorhead 3'3, in the fashion described above and illustrated in Fig. :1. A fur- -ther radialdur-np -port 68. similarly connects the bore V45 at .fa relatively elevated point therein with atmosphere or a suitable .low pressure receiver .tor ,the liquid- ;which is dumped in. the operation 'of .the valve. The tubular by-pass element .'60 includes aan integral, upwardly projecting., sleevelifloe stop portion 69 :adapted tor engagement with va depending :skirt 10 fon the plug 46 atthe uppermost'-gpoint-in the 4axial l:travel `of said koy-pass elementen.

, lnoperation, let it be yassumed that in the ,position ofthe parts Yshown in Fig. 2, the valve ,n.40 .is infful'ly dumped position, i. e., thathydraulic pressure in the clutch controlcyl-inder .26 has `beenfdropped to zero by dumpingy through the llcond-u-itwM, port 61, interior-of Joy-ness element :54), .bore-45, and out the dump port 68.` ln this ,position-of the parts, the seat .54 of valve .53,is positively engaged with the seat 55, by bell crank .49 acting-on the ,stem 48, to -shut on the ,supply of jpressureliquid through inlet 51 to the valve .bore.-45. Accordingly, the conduit 4I is connected with ,dump port 68, through the ,space between :seats 6.1, :62, .to void the clutch cylinder 26.

.It the operator now fully releasesbell crank .49, full hydraulic pressure of about '80 ,pounds per square inch is effective on check member '59 to open .communication of the. pressure. source .with the .passage .516., and said pressure is effective directly on the end of the valve element 4ii?. 'Said .element is thus elevated lto engage its .seat `6.2 against .thefseat 6l on by-pass element 5t. The pressure is simultaneously communicated through .port 61 and conduit 'lll with the .clutch cylinderl., with the result that the clutch is fully applied to positively lock the drums 1|, 2l for rotation .as aunit.

cWhile this 'is taking place, the two elements 53,

' 6U .are urged as. va `'unit upwardly against the )force of spring 63 said upward vtravel of the .elements '53 BD being limited .only by the engage- .ment of vthe sleeve portion `69 of .the latter with the depending stopv skirt 'I0 of plug 46. lWhen this .takes place, the clutch I0 is fully engaged in 'its normal, hydraulically actuated condition, against the force of Belleville spring l3l).

A ilssurnng now that it is desired to produce slight. slip between the clutch disks, vwith yan attendant proportionate relative rotationY of drums; 1 -I, 2 l, the bell crank Il?! is actuated clockwise aA predetermined amount to depress `valve stern'48, thereby cracking thev elements 53, V6I) at the seats',l,"'!5'2, as'illustrated in Fig. 3 in dotted lines. A certain volume. .of hydraulic liquid is immediately by-passed in the reverse direction fromychamber 26 through conduit 4I, vport El, the interior yof the by-pass element 611), valve seats El, 62, and dump port 38.. The spring 63 ,actson lay-pass valve element '6'0 with its lmaxi-- mum orceat this time, but does not seal the seat .6J of theelement against .the vseat l't2 of valve element 53, .since the vpressure .of the hydraulic operati-ng liquid through intake port or passagey opposes the spring. torce, in lay-passing through the space between valve ceats,.l;.,z..2fto the :dump po1t..6:8. Suchpassing bleeds-the full-line pressure, thus 'maintain-ing the clutch engaging pressure, communicated through port iii' at the Spring $33 in eiect variably meters or calibrates desired reduced value.

the venting of pressure between seats 6l, 62 in accordance with its degree of compression. This condition obtains until the actuated downwardly for afurther pressure drop or, if desired, the bell crank lli] is released, enabling line pressure to again elevate'the elements 53, B to whatever extent is desired.

Sleeve-like by-pass element 6B floats in `valve bore 45, within relation to the valve element 53, regulating the amount of intake pressure which is by-passed to dump port 68 andgradually reducing clutch engaging pressure, as described above, until it comes to rest against the lower end of valve bore 4'5, at which time valve element 53 seals oil the intake pressure. At such time the space between seats Bl, 62 is' fully opened, and a zero clutch pressure condition is reached by voiding from intake port G1 past those seats to dump port B8.

The above described regulation of hydraulic pressure by manual operation to dump a desired pressure increment, followed by automatic spring re-sealing of the valve, affords a highly flexible and versatile control device operating on the principle of variable pressure reduction, as contrasted with variable pressure increase. The

parts are exceedingly simple, .rugged and satisfactorily operative over a long life of service.

The modified embodiment illustrated in Fig. 4 operates on the identical principle as the form described above. In this form, the tubular casing 1c is connected with the mechanism to be controlled through a lateral inlet fitting 'il in the form of a boss which is appropriately bored and tapped for communication of the clutch cylinder 2G with the main valve bore 12. The tubular by-pass plunger 'i3 has an O-ring 14 disposed in an annular groove 'iii therein to effect an absolute, leak-proof seal between the same and the wall of bore 12. Said tubular plunger 13 is urged downwardly by means of a coil spring 11 encircling the reduced upper end portion thereof, said spring bearing at its upper end against the cylindrical plug 'i8 in the upper end of bore 12. The upper portion of the tubular member 13 serves as a pilot element, designated 19, which is axially guided for sliding movement by said plug 13.

The reference numeral St designates the elevated liquid dump port of the valve, which is communicated with the interior of the tubular plunger member 'i3 through a port Bl in the reduced portion of the latter. receives the operating stern 82 of the valve, which is controlled at its upper end by a manually operated bell crank 53. Stem 82 is reduced in diameter at 8d to provide a iiow passage 85 bctween, the stem and the element 13, through which liquid is voided by port 8| to the exterior of member "i3, thence to dump port 8U. At its lower extremity the stern S2 carries a cylindrical valve element B having an annular seating ring 81 applied thereto. Said ring is adapted for sealing engagement with the lower annular valve seating surface 38 on the element 13 immediately surrounding the inlet to passage 85. By-pass member 'i3 is normally supported in its fully extended position in the bore 'l2 by an annular skirt extension te engaging the bottom of said bore, said skirt extension being apertured at S0 for communication of the interior thereof with the clutch provided with a spring urged ball check V92. Y

valve stem 43 is again Member 'i3 slidably "'Thez operation of this modified form generally follows the operation of the embodiment of Figs. 2 Aand 3. Successive manual actuationr of the stem B2 results in unseating of the seating ring 81 from the coasting seat 88, thereby dumping yhydraulic operating fluid through the conduit 4i, port 1I, opening 90, passage 85, and ports 8| and $0.' The attendant reduction in pressure is immediately followed by spring urged re-seating of said seat 33` against the ring 81 to maintain the reduced pressure. Release of the bell crank 83 results in upward return of the elements 86 and 13 to their elevated, full line pressure position.

As stated above, the graduated pressure release valve of the present invention was specially devised for installation in association with a steering clutch for an endless track or crawler type of tractor, characterized by dual power shafts controlled independently of one another to govern the driving and steering of the tractor. Figs. 5 and 6 show an installation of this type. It may be considered that the separately illustrated housings i6, i6', disposed on opposite sides oi' the central drive gear l5, enclose identical hydraulically controlled clutch units such as the unit l shown in Fig. l. These units serve to control the variable slip drive of the respective output shafts to which the track bull pinions are connected. The arrangement is similar to that illustrated and described in my copending application Serial No. 778,382 identified above, in that the operation of `the respective hydraulically controlled clutches is coordinated with the application of the brake band B to the outer clutch drum 2 l. The sole difference is that in the present installation there is but a single operating lever and linkage assembly for each of the clutch units. This is distinguished from the dual operating assembly required in the construction of said application due to the planetary character of the mechanism illustrated therein. By the same token, certain lost motion provisions in the operating linkage are omitted in the present control structure shown in Figs. 5 and 6.

The bell crank operating member designated 52 in Fig. 2 is represented in Fig. 5 as a connecting rod which is pivoted to the bell crank 4S. This rod is operatively connected, by means of a lost motion coupling 95, an encircling spring 91 and a further rod 93 secured to coupling 96, with the free end of a toggle-type brake actuating arm 99. Said arm is in turn operatively connected to brake band B by more or less standard provisions, generally designated M10, in such manner that a counterclockwise actuation of arm 99 results in application of the brake band B to the outer control drum 2l of the clutch unit lll. An actuating link ll is' pivoted at its ends to arm S9 and to the manual control lever lil?! to operate the brake arm 99 and the control valve 44.

The relationship of the above parts is such that swinging of lever m2 in the counterclockwise direction, as viewed in Fig. 5, results in release and upward retraction of valve control stem 48 of the pressure reduction valve 44, with the result that full hydraulic line pressure is applied to the clutch unit It to engage the same and efect a direct drive connection from drum il to drum 2l and shaft 38. Under this condition, brake band B is fully withdrawn from drum 2l to allow free rotation thereof, prior to engagement of the clutch. Upon manipulation of lever H32 in the opposite, clockwise direction, the aforesaid valve stem 48 is depressed, the hydraulic pressure in clutch cylinder 26 is reducedvlto .an extent proaccesso perdonare to' the amount of vkdow-mmm''depression'of the-stem, andtheBel-leville spring."returns-r clu'tcrpressure piston. 25 tol proportionably re.-

duce 'the friction force on the clutch'disk's.

Accordingly, when the operator ofthe tractor desires tomalreibutl'a whichf 'controlsn the which the turn is to'- be made. IDu'ez tothe normal radiali clear'axrcev'between brake band? B. and; the. drum. 2 I`,v the i'nitial resulting movement of link` Suclr pressureA reor-large, is propor- A tionately reflected-in the. amount ofrslip betweenz' 158,. I.9r,. and. rotation of outer drum;k Zelo-relativer to the inner drivingdrum: tl" of" the clutch disks` clutch im? Hence; since-said outer drum' is rigidly- If a: dead trackor iullpi-vot turnY isdesired, lever IIlZziszfullyf actuated clockwise toiully dump the pressure` andz tostopz' drum'. 2J'A and thas-hatt 33.` towh'ich it is; connected. The; aforesaid vbrake band clearance permits! the clutch-` tobe fully clisen-v gaged before the drum 2| isv braked-.suiciently to haltthe-.same` lever Ill-24s again manipulatedin the counteroloclrvvr-is@:V direction, the brake.

band is. released and the clutch Variably re-enraged depending* upon. the.- extent v of the said. manipulation;l of. the lever and resultant pressure urged .frerengagementof its. disks. t8', I9.

Theprovisionof aneicientcheclc valve struc.- ture ofsthe typeegenerally designated.. 53 in Figs. 2 andyisot considerable. importance ina steering. clutch; install-ation, of the. type. described, not. only to= the extent that; it. controls the individuali 'op-- erating characteristics. of the valve of. which it'. is a. part; butalsa because thischeckin. effect functions as: a pressure control. and regulator. for'tlle other valve 44" of. thedual installation. and its associated clutch.` Ina'srnuchas tlltwo. pressure inlet ttings 51 5:1 are connected/to a common source of hydraulicpressurefl'iquid, a voidingA of the' pressure in one clutcliunitwouldtend toresul-t inl a` reduction of. the full line pressure intended to. befeffective'on the. other unit.`` These check members are in. addition: to the normal regulator valve (not. shown) through' lwhich' the systemis supplied. with hydraulic pressure from the pump or other source.;` y v In. the form Aill'ustratjed in, Fig.. v2, the checl' vafve'j 59"`comp`ris`es an elongated cylindrical" plugj I'05 which slidabIy'ts' the.` bore oi'inle't fitting 51" said, plugl being.' piloted-l in an' integral' cylindrical extension.' I Uli oftting 5T which" is. received in' a cylindrical transverse bore 'IUT of the valve cas; ing,` 4'4. The'checkmember is urgedfto the left by'a. coil'spring'" IUHin said' lastnamed boresaid spriligf surrounding, a. rearwardly' extending.` Ipin I'US" on'tlie check member and abutting' a' shoulder II'II'on the latter; 'The opposite 'endA of said spring abut's an aperturedretainer II.' which is secured to the. housing. v

InV addition to the'abovfe features-of improved construction" and operation of' t-lre above; assenr. b'yt;

present invention presents various -improi'fed specific s'tru'c'turall features. TI-res'e deal"v particu" gradual turn,"herocks, to a sliht degree-in clockwise direction-L. tlie lever |02 side ofthe? tractor toward will slightly.vl depress valve; stem. d8. willk The pres;-

inV a. generali` 'or 'organizational sense;` the shaped,

` v:face of end trol' of sub-assemblies associated therewith. Such details areillustrated. in- Fig. l oi thedraw.- ings-g te which attention is: directed.

Itwill benoted thatthefinternal'splined clutch l druml II is secured to an outwardly extending flange II5 of the driving-ring I3; 'by means of. 10i bolts` I F6, and that said druml is circumferential.'-

ly'reeessed internally of its outer' periphery at'I IfI 1.v

toprovide van vaal'ilnlil'apilot shoulder which tele-r flange'r IIIE'J. The outer splinedi" scopes over said control drum 211' fi's constructed separate from. the:

thereof, lbeing 'rigidi bolts I? I 8l' atadliacent 'radial flanges of. said. drum. and endplate'.l Vmillar shoulder I1 I'll'maellined'on 'the right-hand plate 21.'

When-litl is desired to remove the assembly ot' clutch drums II, 2|, abutment or backing plate 22, pressure member Itv andI theclutch disks |18, I9 from the unit'i as for servieingyrepar or re.-

"251 lacement of arts, this" isf sim l and uickl f connected tothe output shatt. 3'8, a proportionate'- p p p y q y reduction in the speed ot the lattertakesfplace;

performed in thefollowing manner: The bolts.

I I6 are removed and the internal' drum4 I I is. slidk to'theleft, as indicated in dotted. lines in Eig, l',

i until its pilot shoulder II If is clear ofy the:- driving "ring lla'ngeA |45. Boltsf theouter drum 2'Il is'. slid'ftosth'e rig-ht'to olea-rift. `from the pilot shoulderiIrIzS of end plate4 21, thus, separating said. drum from said end plate andv further telescopina III' and:- .-Ir relative to 35" one another. Assuming that the brakew bandi B- the casing, piloting external drum. 2:IA on. endzplatev .45. pilot shoulder" I`I9,. bolting: said. drum to. the end pla-t'e,` and piloting and; bolting. the internal drum onth'e'di'fivngf flange- I\I.5.V Thisv last namedv operation is: facil-itated'by theA provisionA or an annularslioulderIZIl on therright-hand external-- 50. periphery et said drum', for: the. reception of a cr-ovvlrlar` or like implement: to assist in shitting the toward-v the right and' over the flange III-5. Tliesejoperations5 of removal andV replacef ment' of thev clutch parts are accomplishedV With- 55. out" disturbing' either'tlre: hydraulic installation totliefleft'v thereof or" the dri-ving components tothe right.

Reifeurinev tollig. 1.1,. itwill' benoted: than the arrnular recessingf of! the hydraulic' piston 25 at Z5" 60...y alfordsa' chamber receiving' the Belleville` spring SITI andi snap# ring 3I byl Whclr. the'latter ist supported" to` act on: tlfrepistoni. Tous the enti-rel hydraul'io`r 'unitI of' tlie`- clutch? is. held. in assembly whenI the above described operations are perfort-nodi.` f' very desirable"overallzcompactncss of structure vis a"- f-urtlfier result..

Referencellas beenf made. tothe provision of' a lost motion feature inthe; connection of the operating leverI'IlZ and: link IU-If to the bell crank Fig; 5i.. This featureis.y required; wheny ar Valve 44 is employed. Spring "91S of: lost motion. coupling.' lltn isoE suillcint strength to transmit the necesisary forceto depress valveistem 48 Without compressing. However, assuming that, due to brake'.

hydraulic cylinder-delfmngf end plate.y 257i clamped tol said plate by` ISI 8i 'are then. removed: andy band wear, to drum 2l at the time the valvevelement 53 seats at 55, further brake-applying movement of link is made possible by the compressing oi spring 91. Such lost motion provision is not necessary in the use of the valve shown in Fig. 4, for the plunger head 86 merely travels further in the axial inlet bore of the valve in the event of continued depression oi valve stem 82.

It is imperative that in the fully seated position of the valve element 53 of Fig. 2, the pressure on the clutch be entirely voided. Therefore, the axial length of the skirt 65 oi by-pass element 6i) is made greater than that of the element 53. This insures unseating of the by-pass surfaces BI, 62 under the condition noted above, which is shown in Fig. 2. With reference to the form of Fig. 4, the ring 8l is properly positioned on plunger 86 for the same purpose oi insuring an opening to the annular flow passage 85 when the member 86 is in inlet-closing position.

I claim:

l. A hydraulically controlled clutch construction comprising coaxial relatively rotatable driving and driven members, clutch elements. mounted in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip oi said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operatively connected with and operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, rom a valve coupling said clutch elements in non-slip relation, and a pressure line communicating said valve with a source of hydraulic operating liquid, said dump valve including coaxial, axially movable valve elements which are axially exposed to the pressure in said line, at least one of said elements being urged axially by said pressure.

2. A hydraulically controlled clutch construction comprising coaxial relatively rotatable driving and driven members, clutch elements mounted in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operatively connected with and operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from a value coupling said clutch elements in non-slip relation, and a pressure line communicating said valve with a source of hydraulic operating liquid, said valve comprising a hollow housing having an intalre port communicating the interior thereof with said pressure line, a discharge port communicating said interior with said hydraulically actuable members and a dump port communicating said interior with a low pressure receiver, a manually actuable valve element shiitable in said housing interior to control liquid flow from said line through said intake port to said interior, and a further spring urged valve element shiftable in said housing with relation to said first named valve element to control liquid communication between said discharge and dump ports.

the band B has not been fully applied f 'hydraulic operating 3. yA hydraulically controlled clutch construe-- tion comprising coaxial relatively rotatable driving and driven members, clutch elements mounted in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump Valve operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from a valve coupling said clutch elements in non-slip relation, a pressure line communicating said valve with a source of liquid, and a spring urged check member disposed in said line between said source and valve and opposing the pressure oi said source, said valve comprising a hollow housing having an intake port communicating the interior thereof with said pressure line, a discharge port communicating said interior with said hydraulically actuable member, and a dump' port communicating said interior with a low pressure receiver, a manually actuable valve element shitable in said housing interior to control liquid flow from said line through said intalre port to said interior, and a further spring urged valve element shiftable in said housing with relation to said first named valve element to control liquid communication between said discharge and dump ports.

4. A hydraulic pressure reduction control valve comprising a valve housing having bore, a pressure inlet opening to said bore and a pair of outlet openings to said bore, one of which is a high pressure port and the other of which is a dump opening, a valve element disposed for sliding movement in said bore to seal said inlet opening from said outlet openings, a pressure by-pass element coaxial with said valve element and slidable in said bore, said elements dening therebetween an annular by-pass port located between said outlet openings, spring means normally urging said elements in a direction to close said port, and manually operable means acting on one of said elements in a direction to open said port. p

5. A hydraulic pressure reduction control valve comprising a valve housing having an internal bore, a pressure inlet opening to vsaid bore and a pair of outlet openings to said bore, one of which is a high pressure port and the other of which is a dump opening, a valve element disposed for sliding movement in said bore to seal said inlet opening from said outlet openings, a pressure bypass element coaxial with said valve element and slidable in said bore, said elements defining therebetween an annular by-pass port located between said outlet openings, spring means normally urging said elements in a direction to close said port, and manually operable means acting on one of said elements in a, direction to open said port, said last named means vurging said valve element in a direction to close said inlet opening, said by-pass port being open when said valve element is in said last named position.

6. A graduated hydraulic pressure reduction control valve comprising a valve housing having an internal bore, a pressure outlet opening to said bore, and a pair of outlet openings, one of which is a high pressure port communicating said bore with a device of which is a dump opening communicating said an internal v to be controlled and the other borev with a lowfpressure receiver,l inletivalueef.

seat in saidV housing; downstream from said' inlet.

opening,- a` valve member slidablyr mounted said=liousing bore for engagement4 withfanct dien..

engagement from saidseat to control: said inlet.

opening, means. to positively actuate saidf val-ve. member axially of saidbore toward# saidseat; saidi valve member shifting: awayv from said'. seatunder pressure in said inlet opening. follovvti-ngzrelease off' saidl last vnamed means; a by-.passrmemioen slidable in said' bore inv coaxial relationr tof! said valve member and dei-ming an annular byspassv path therebetween from-said. inlet. opening-to said dump openingysaidl valve and'. byi-'pass mem.`

bers having--coactingannula-rseating surfacesren--a gageable to seal= said path, andlspringmeansurg-e ing said-seating surfaces; in a, direction for. ens;

gagemen-t, said valve and ley-pass elernentsibe@l ingshifftable-asa unit awa-y `from saictinletseat' by pressure iii-said inlet openii-igwhen said 'acm' tuatin-gfmeans iis released.

7.' graduatedv hydraulic pressure reduction control valve comprisingA a valvehousing; having an internal bore, an inlet opening adapted tocom-e municate said borewithasource offoperatilng liquidunderpressure,and a pair of outlet openings normally communicating said' borerespec tively With'a.` device to be controlled and'- with a lowl pressure receiver, any inlet valve seatfin'- saidhousingV downstream from; said` inletopening,l a

valve member slidably mounted in said'housingff bore "for engagement with and disengagement from said seat,-I means to posi-tivelyl act-nate said valve member axiallyoisai'd' boretoward"andinto-A engagement with 'said 'seat,j said'l Valve disengaging and'shiftin'g away from saidseat under pressure from said` source. following; release of said lastnamed means, a byj-pass member' slidablej in said. bore in, coaxial relationjto said valvegrnemirben, said'. valve and. bil-pass. members 'having 'c0- actingV seating surfaces adapted to. engage' to c ut ofl; communication of said. inlet opening with said'z bore. andvvith` said receiver outlet o izieninl.` and, spring means urgingI said` seating surfaces in a direction for said' engagement, said valve'and` byfpass elements` being shiftable, as, aA unit. away fro'mlsaidinlet Seatbyj pressure. from said source when said. actuating means is released.

`8.vv A` graduated hydraulic pressure reduction: control, valve comprising a .valve4 housing having. an: internal` bore, an inletA opening adaptedtoi. communicate `saidbore with, asourceffof operatingy liquid under pressure, and` apair. of outlet open,- ings normally communicating said;- borer respeta.. tivelyfwitha device to becontrolled and with a lovvpusessureI receiver, a springl `urged: check. menfiberty operatively', associated with saidfinlet opening,l to;

open the .latter `for communication Withsaid borel only at full operating liquid pressure, an* inlet v ralve seat insaid housing downstream from said inletp opening, a. valve, member slidablyy mountedin said-housing bore,y for engagement-With and dise..

engagement` fromvksaicl seat; means-to positively.`

ber slidablein said bore in coaxial.; relation tos said2 valve member, said valve and. by-passmem-- bers)l having, enacting. seating.surfacesndaptedgto; engaget to cutv oli communication:A of; said, inleti Opening with said boreandiwith-said receiver. ou Morgaine..Sprinsmeansfureinasaidseatines {8S-@S1 im redirection; fpnsaid engagements; s

adi i5 i4 value..A and. .by-.epass .elements being shirtabley asia. uniti-awayfrom said inlet'y seat by pressure., from said, sourcefwhen said actuating means. is'` released".

91 yA.L hydraulic; pressure reduction control valve.r comprising a valve housing having an` axial: bore; anaaxiallyl disposed inletopening adapted to come Imznicate'said' bore with a source of operatingl liquid .under pressure and a pair of outlet opening'sspaced: axially from said. inlet opening, one ofV which is adapted` to be communicated Withl a member toibe,` controlled and the otherV of which is alovir pressure.4 dump opening, a manuallyz actirable valve element shiftable axially toward'andvv 1' adaptedLto-.seal' saidx inlet opening, a tubular by'- pass element i-ntelescoped external relation tosaid?A valve element, said valve and by-pass'- elements dening therebetween an annular ley-pass lportfto said bore andi' being 'engageable with-one anotherito;` cl'ose saidll port, spring means: urging sai'debyepassI element in a direction for-port seal-- ing:v engagement` with saidL valve element. said controlled member-K outlet opening and dump out# let-openingcommunicating freely with said borey onthefrespective-downstream and upstream sidesof saiclvport,y whereby` to dump operatingl liquid; fronfiwsaid controlled member-through said portv and dump-opening whenv sa'idf elements are dis-` engaged 1'0. A graduated pressure release and' controlu valve-comprising a valve housing havingV an in'- terna'l@ chamber, an inlet"` openingr to said cham? beradapted to be connected-to a source of'liqui'dL undenpressure; a supply" opening adapted to be connected with a device` to becontrolled',r anda dump opening; said* housing having a control portV between said inlet-,opening and supply opening, a pair` of valve elements mountedlfor movement relative to one another in,y saidrcharnber, oney of said valve elements being engageable and disen-l gageable with said port to control the same, said, elements bei-ng engageable and" disengageableY with one another' upon said relative movement` tlrereoff` to open and close a dumpA path therebeeen' fromjsad' supply 'opening to said dump opening; means resiliently urging said, valve elements to closesaid dump path, and. manually op,- erlle means actuatingisaidelements :to open said pa -f Il,I A, graduated, pressure release and. control valvecomprising. aA valve housing having an. in ternal chamber,Y aninlet opening tosaid chamber adapted tobe connected. to. a source of. liquidP under pressure, a 1 supply opening adapted tcv be,- connected', with a/device. to.. be controlled, and a dump opening,v said inlet `opening. beingfin. normalcommunication with, said supplyv opening, said housing having a control port between said in-v letlopeningf and supply opening, a pairvof valve elements mounted for, movement relative-to one another-in. saidchamber, one of saidvalvel ele-` ments beingengag-eable and. disengageable-with said-inertie. control the same, said; elements being; engageable.A andv` disengageablewith` one another upongsaidrelativemovement thereof. toppen and. close afdump paththerebetween fromsaid suppli` opening,l toisaiolt clump opening,A meansresilient-lyurgingone of` said valve elements ina. direction'` 13o-close saiddump path, and manuallyoperable meansactna-ting the kother of saidv elements-in the` same direction to opensaidpath, said: other'y element being shiftableby said: last-named means@ toiclosefsadanlet onennal 12 A, graduated; pressure release# and'contmli cpmpIusinglai valve housing -s having;I ani-inlr ternal chamber, aninlet openingv tosaid cham` engageable with one another upon said relative movementthereof to'open and close a dump path therebetween from said supply opening tosaid dump opening, means resiliently urging'saidfvalve elements to close said dump path, manually operable means actuating said elements to -open said path, and a spring urged check member controlling inlet opening on the downstream side thereof` v i -`A13. A hydraulically controlledsteering assembly'A comprising a pair of coaxially arranged clutch constructions, eachfof said clutch constructions comprising coaxial relatively rotatable driving and driven members, clutch elements 'mounted in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from-a valve coupling said clutch elements in non-slip relation, a pressure line com- -1 municating said valve with a source of hydraulic operating liquid, and a spring urged check member disposedY in said line between said source and valve and opposing the pressure of said source, said valve comprising a hollow housing having an intake portY communicating the interior thereof with said pressure line, a discharge port communicating said `interior with said hydraulically actuable member, and a dump port communicating said interior with a low pressure receiver, a manually actuable valve element shiftable kin said housing interior Ato control liquid now from saidline through said intake port to said interior, and a further spring urged valve element shiftable in said housing with relation to said first named valve element to control liquid communication between said discharge and dump ports, the said source with which the respective pressure lines communicate being common to said pair of clutch constructions and the respective rotatable driving members being drivingly connected to a common driving device. p

14. A hydraulically controlled clutch construction comprising coaxial relativelyrotatable driving and driven members, clutch elements mounted in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from a valve coupling said clutch elements in non-slip relation, and a pressure line communicating said valve with a source of hydraulic operating liquid, said valve comprising a hollow housing having an intake port communicatingthe interior thereof with said pressure line, a discharge, porticommunicating said interior with said hydraulically actuable member, and a drump port communicating said intake with a low pressure receiver, a manually actuable valve element shiftable axially in said housing interior to control liquid now from said line through said intake port to said interior, and a further spring urged valve element shiftable axially in said housing into and out of engagement with said first named valve element to control liquidV communication between said discharge and dump ports.

15. A hydraulically controlled clutch construction comprising coaxial relatively rotatable driving and driven members, clutch elements mounted in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative slip of said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compressthe same, a graduated y'pressure dump valve operable to reduce pressure on said-hydraulically actuable member in successive increments, during a'given valve operating cycle, from a valve coupling said clutch elements in non-slip relation, a pressure line communicating said valve with a source oi hydraulic operating liquid, and a spring urged check member disposed in said line between said source and valve and opposing the pressure of said source, said valve comprising a hollow housing having an intake port communicating the interior thereof with said pressure line, a discharge port communicating said interior with said hydraulically actuable member, and a dump port communicating said interior with a low pressure receiver, a manualy actuable valve element shiftable axially in said .housing interior to4 control liquid flow from said line through said intake port to said interior, and a further spring urged valve element shiftable axially in said housing into and out of engagement with said irst named valve element, to control liquid communication between said discharge and dump ports.

16. A hydraulically,controlled steering assembly comprising a pair of coaxially arranged clutch constructions, each of said clutch constructions comprising coaxial relatively rotatable driving and driven members, clutch elements mounted in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative slip or said members in'accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from a valve coupling said clutch elements in non-slip relation, a pressure line communicating said valve with a source of hydraulic operating liquid, and a spring urged check member disposed in said line between said source and valve and opposing the pressure of said source, said valve comprising a hollow housing having an intake port communicating the interior thereof with said pressure line, a discharge port communicating said interior with said hydraulically actuable member, and a dump port communicating said interior with a low pressure receiver, a manually actuable valve element shiftable axially in said housing interior to control liquid ow from said line through said intake portto Asaid interior,

17 and a further spring urged valve element shiftable axially in said housing into and out of engagement with said rst named valve element to control liquid communication between said discharge and dump ports, the said source with which the respective pressure lines communicate being common to said pair of clutch constructions and the respective rotatable driving members being drivingly connected to a common driving device.

17. A hydraulically controlled clutch construction, comprising coaxial relatively rotatable driving and driven members, clutch elements in nonrotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance With the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operable to reduce pressure on said hydraulically actuable member in successive increments, during a given. valve operating cycle, from a valve coupling said clutch elements in non-slip relation, and a pressure line communieating said valve with a source cf hydraulic operating liquid, said valve comprising a hollow housing having an intake port communicating the interior thereof with said pressure line, a discharge port communicating said interior with said hydraulically actuable member, and a dump port communicating said interior with a W pressure receiver, a manually actuable valve element shiftable axially in said housing interior in a direction to close said intake port, a further valve element shiftable out of engagement with said lirst named valve element to control liquid communication between said discharge and dump ports, and a spring acting on said further valve element to oatingly oppose the pressure of said source on said further valve element, which acts to urge the latter out of engagement with said first named valve element when said intake port is opened by said iirst named valve element.

18. A hydraulically controlled clutch construction, comprising coaxial relatively rotatable driving and driven members, clutch elements in nonrotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from a valve coupling said clutch elements in non.- slip relation, a pressure line communicating said Valve with a source of hydraulic operating liquid, and a spring urged check member disposed in said line between said source and valve and opposing the pressure of said source, said valve lcomprising a hollow housing having an intake port communicating the interior thereof with said pressure line, a discharge port communicating said interior with said hydraulically actuable member, and a dump port communicating said interior With a low pressure receiver, a manually actuable valve element shiftable axially in said housing interior in a direction to close said intake port, a further valve element shiftable axially in said housing into and out of engagement with said rst named valve element to control axially in said housing into and liquid communication between said discharge and dump ports, and a spring acting on said further valve element to iloatingly Oppose the pressure of said source on said further valve element, which acts to urge the latter out of engagement with said rst named valve element when said intake port is opened by said first named valve element.

19. A hydraulically controlled steering assembly comprising a pair of clutch constructions, each of said clutch constructions comprising coaxial relatively rotatable driving and driven members, clutch elements in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from a valve coupling said clutch elements in non-slip relation, a pressure line communicating said valve with a source of hydraulic operating liquid, and a spring urged check member disposed lin said line between said source and valve and'opposing the pressure oisaid source, said valve comprising a hollow housing having an intake port communieating the interior thereof with said pressure line, a discharge port communicating said interior with said hydraulically actuable member, and a clump port communicating said interior with a low pressure receiver, a manually actuable valve element shiftable axially in said housing interior in a direction to close said intake port, a further valve element shiftable axially in said housing into and out of engagement with said rst named valve element to control liquid communication between said discharge and dump ports, and a spring acting on said further valve element to iioat'mgly oppose the pressure of said source on said further Valve element, which acts to urge the latter out of engagement with said ilrst named valve element when said intake port is opened by said iirst named valve element, the source with which said respective pressure lines communicate being common to said pair of clutch constructions. 20. A hydraulically controlled steering assembly comprising a pair of clutch constructions, each of said clutch constructions comprising coaxial rotatable driving and driven members, clutch elements in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance with the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operable toreduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from a valve coupling said clutch elements in non-slip relation, a pressure line communicating said valve with a source of hydraulic operating liquid, and a spring urged check member disposed in said line between said source and valve and opposing the pressure of said source, said valve comprising a hollow housing having an intake port communicating the interior thereof with said pressure line, a discharge port communicating said interior with said hydraulically actuable member, and a dump port communicating said interior witha llow pressure receiver, a manually actuable valve element shiftable axially in said housing interior in a direction to close said intake port, a further valve element shiftable axially in said housing into and out of engagement with said kirst named valve element to control liquid communication 'between said discharge and dump ports, and a spring acting on said further valve yelement to floatingly oppose the pressure of said source on said further valve element, which acts to urge the latter out of engagement with said first named valve element when said intake port is opened -by said first named valve element, the source with which said respective pressure lines communicate being common to said pair of clutch constructions and the respective rotatable driving members being drivingly connected to a common driving device.

2l. In a hydraulically controlled steering clutch, a pair of like, coaxially disposed, rotative l clutch units, a common driving member operatively connected to said units, said units each including a hydraulic control device having ahydraulically cperated'member which normally acts to drivingly engage said clutch unit, a variable pressure reduction valve Yfor each of said units, said valves being supplied by a common source of hydraulic pressure liquid and being operatively connected to said respective clutch control devices whereby to normally impose a predetermined minimum operating pressure on said member thereof, operating means for each of said valves to divert liquid from its respective control `device through said valve to a lower pressure to thereby release said respective associated clutch unit, a spring urged check member associated with each'valve between the same and said source and yieldable only under pressures at or above said minimum operating pressure, whereby upon operation of the associated valve to prevent undesired dropping `of pressure in the control device associated with the other valve, a brake operatively associated with each of said clutch units to retard the same, means for actuating said brake, and common means for actuating the valve operating and brake actuating means of said respective units in sequence.

22. VIn a hydraulically controlled steering clutch, a pair of like, coaxially disposed rotative clutch units, a common driving member operatively connected to said units, said units each including a hydraulic control device -having a hydraulically operated member which normally acts to drivingly engage said `clutch unit, a variable pressure reduction valve for each -of said units, said valves being supplied by a common source of hydraulic pressure liquid and being operatively connected to said respective clutch control devices whereby to normally imposeapredetermined minimum operating -pressure on said member thereof, each or" said valves including a pair of coacting, relatively movable-elements `deiining therebetween a liquid dump 'path from said associated control device to a low pressure discharge, a spring `resiliently urging said valve elements in a direction to close said path, and valve operating ymeans 'to open said path, whereby to divert liquid from the associated control device to said low pressure'discharge vand thereby release the associated clutch unit, a spring urged check member associated with each valve between the same and said source, said check member vbeing yieldable only under -pressures at or above said minimum operating pressure,

whereby upon operation of the `associated valve,l

Vsaid clutch unit, a common source of `having an to prevent ,undesired -.dropping lof lpressure .in the control device associated .with the other valve, :a brake `operatively associated Awith each of said clutch units to retard `the same, means vfor actuating `said brake, and common means for actuating the valve operatingand brake actuating means of said respective units in sequence.

25. A hydraulically controlled clutch assembly comprising a pair oilike, coaxially disposed-clutch units, a common driving member operativelyconnected to said units, said units each including a hydraulic control device having a hydraulically operated member which normally acts to drivingly engage said clutch unit, a common source of hydraulic operating liquid for said control devices, a variable pressure reduction valve interposed between each of said units and said common hydraulic source, which valves control the variable slip coupling eiected by said respective clutch units by graduated reduction over a substantial range of the pressure applied thereon from said source, each of said valves comprising a housing having an inlet opening connected with said source, a pair of outlet openings, one of which is connected to the hydraulically operated member of the respective clutch unit and the other of which functions as a low pressure dump opening, a valve element controlling said inlet opening, a by-pass element engageable and disengageable with said valve element and adapted to communicate said outlet openings with one another when said elements are disengaged, spring means normally urging .said elements for engagement with one another, and means to operate said valve member to control said inlet opening, and a resiliently urged check member associated with each of said pressure reduction valves between the same and said common hydraulic source, which check members are yieldable at or above minimum operating pressure fer the respective hydraulic control devices, whereby upon operation or" one valve to prevent undesired dropping of pressure in the control device associated with the other valve.

24, A hydraulically controlled clutch assembly comprising a pair of coaxial driven members, a separate clutch unit drivingly connected to each of said members, a common driving member operatively connected to said clutch units, a brake engageable with each of said members to retard the saine, said units each including a hydraulic control .device having a hydraulically operatedI member which normally acts to drivingly engage hydraulic `operating liquid for said control devices, a variable pressure reduction valve interposed between each of said units and said common hydraulic source, each of said valves comprising a housing inlet opening connected with said source, a pair of outlet openings, one of which is connected to the hydraulically operated .member of the respective unit and the other of which functions as a low'pressure dump opening, a valve element controlling said inlet opening, a b y-pass element engageable and disengageable with said valve element and adapted to communicate said outlet openings with one another when said elements are disengaged, and spring means normally urging said elements .for engagement with one another, a resiliently urged check memberassociated with each of said pressure reduction valves between the same and said source, which check member is yieldably at or above minimum operating pressure for the respective hydraulic control devices, individual actuators -for said respective valve elements operative to control said re spective valve inlet openings, and means to operate said respective actuators operate said respective brakes in synchronized relation thereto.

25. A hydraulically controlled steering assembly including a pair of clutch constructions each comprising coaxial relatively rotatable driving and driven members, clutch elements mounted in non-rotative relation to said respective members and adapted to be compressed to rotatively couple said members, said coupling varying as to relative rotative slip of said members in accordance With the force of said axial compression, a hydraulically actuable member acting on said clutch elements to compress the same, a graduated pressure dump valve operatively connected with and operable to reduce pressure on said hydraulically actuable member in successive increments, during a given valve operating cycle, from a valve coupling said clutch elements in non-slip relation, a common source of hydraulic operating liquid for said clutch constructions, and a pressure line communicating said dump valve with said source, said dump valves each including coaxial, axially movable valve elements which are axially exposed to the pressure in said line, at least one of said elements of each dump valve being urged axially by said pressure.

26. A steering assembly in accordance with claim 25, in which a resiliently biased check valve is provided in said pressure line between said including means to References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 382,643 Fox May 8, 1888 728,572 Hanson May 19, 1903 876,543 Hanson Jan. 14, 1908 1,298,956 Johnson Apr. 1, 1919 1,566,111 Miller Dec. 15, 1925 1,864,126 Ferris June 21, 1932 1,872,250 Coughtry Aug. 16, 1932 1,897,432 Klotzman Feb. 14, 1933 1,910,084 Bixby May 23, 1933 1,932,039 Hewitt Oct. 24, 1933 2,077,988 Cossey Apr. 20, 1937 2,098,342 Knutzen Nov. 9, 1937 2,151,153 Rode et al Mar. 21, 1939 2,191,669 Kress Feb. 27, 1940 2,282,143 Carter May 5, 1942 2,328,606 Boldt Sept. 7, 1943 2,412,436 Vanderzee Dec. 10, 1946 2,437,670 Adamson Mar. 16, 1948` 2,501,706 Bent Mar. 28, 1950 FOREIGN PATENTS Number Country Date 24,189 Great Britain 1912 507,673 Germany Aug. 9, 1927 552,640 Germany May 26, 1932 

